Starting phase-converters.



E. F. W. ALEXANDERSON.

' STARTING PHASE CONVERTERS. APPLICATION FILED AUG: 1. I916- RENEWEDJAN. 29. me.

1 ,3QO,545. Patented Apr. 15,1919.

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AWE 29 Inventor-I Ernst .fllexander'son;

by E His fitter-neg.

UNITED STATES PATENT V OFFICE.

ERNST I. w. ALEXANDERSON, OF SCHENECTAJJY, new YORK, AssIGNon 'roGENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STAR-TING PHASE-CONVERTERS.

Specification of Letters Patent. Patented Apr. 15, 1919.

Original application filed January 2 9, 1914, Serial No. 815,280.Divided and this application filed August 7, 1916, Serial No. 113,483.Renewed January 29, 1919. Serial No, ,f73,929.

ing and exciting a dynamo-electric machineused as a phase converter.

It is well known that polyphase dynamoelectric machines may be utilizedas phase converters by connecting one phase of their armature'or primarywindings to a single phase source or supply, and then taking polyphasepower from all of the windings. Such machines are, however, not"self-starting and some means must be provided for brlnging them up tospeed. It is common also to provide such machines with afieldsynchronousl excited.

My invention relates to the operation'of dynamo-electric machines whichare'not selfstarting, and particularly to a novel method and apparatusfor starting and exciting a dynamo-electric machine used as a phaseconverter. Another-feature of my invention comprises a novel arrangementfor stabilizing the action of a series generator which is used as anexciter for the dynamo-electric machine, and for stabilizing the latteras well as facilitating its falling into step when started.

This a plication is a division of In application, erial No. 815,280,filed; anuary 29th, 1914, wherein is described anovel system of controlfor the utilization of phase converters in supplying current topolyphase motors.

My, invention will'be more readily understood from the followingdescription, when taken in connection with the accompanying drawing, inwhich Figure 1 is a diagram showing the apparatus employed andconnections used; Figs. 2 and 3 are diagrams showing the resultingconnections during the steps of my method.

In the utilization of my invention, power will be supplied from anysuitable source, for example, through the trolley 10 and the winding bymeans-ofwhich they may be line switch to the primary winding 16 of atransformer '15. The secondary winding 17 of the transformer is providedwith taps l8 and 19, by means of which a reduced voltage may be suppliedfor a purpose which will later appear. The dynamo-electric machine 20here used as a phase converter is illustrated as a two-phase machine,provided with primary windings 21 and 22, here shown as mounted upon thestator, and with a secondary member '23 which is provided with asquirrel cage winding 24 and a field winding 25, to which current may besupplied by means of slip rings 26. It will be understood that myinvention is equally applicable to a phase converter of any number ofphases. Mechanically connected to the rotor of the phase converter 20 isan excit'er 30, which is conveniently provided with two field windings31' and 32 which are wound in opposition, said exciter being also pref;

erably provided with a commutating field winding 3'3. An adjustableresistance 27 is provided in the circuit of the field winding 25 and Ihave shown mains 28 and 29 leading from the windings 21 and 22respectively, by means of which power may be supplied to polyphasemotors or other apparatus. The

connections necessary for utilizing my invention are preferablyefi'e-cted by means of a controller 34 throu h the agency of theconnections illustrated in Fig. 2, from which 1- it will be seen thatthe armature of the ex-.

phase converter and bring the same approximately to synchronous speed.After a suitable interval, the controller 3& may be moved to its secondposition, thereby causing the energization of the windings of thecontactors 36 and 37. The closing of these switches will connect thewinding 21 of the phase converter across the whole of the secondarywinding 17 with the transformer. bince the phase converter has alreadybeen started, it will now run as a single-phase induction motor becauseof the provision of the squirrel-cage winding 24 and drive the exciter30 as a generator. The movement of the controller to this secondposition will have caused the denergization of the winding of thecontactor 35, thereby disconnecting the exciter 30 from the source ofsupply and causing the energization, through an interlock on thecontactor 35, of the windings of the contactors 38 and 39. The 010- sureof the contactor 38 will connect the exciter 30 in series with its fieldwindings 32 and 33 and the resistance 27 to the slip rings 26, therebycausing the same to act as a generator and furnish current to the fieldwinding of the phase converter. The closing of the contactor 39 willshort-circuit the motor field winding 31. Obviously, the provision oftwo field windings 31 and 32 which are wound in opposition is notessential but is for convenience of operation, since each winding maythen be designed with the desired ampere turns and the desired currentcarrying capacity. However,

1 by providing a short-circuit around the field winding 31, I make theexciter voltage less sensitive to fluctuations of current, or in otherwords give the exciter the characteristics of a shunt generator. Anycondition of hunting which may exist will, if the exciter is a seriesgenerator, induce pulsating currents in the exciter field winding, andthese pulsations of the current will result in corresponding pulsationsof voltage. These in their turn would increase the original pulsationand might make the oneration of the whole apparatus unstable. Such ashortcircuit as I have provided will prevent any appreciable pulsationsof the field flux and -will increase the facility with which the phaseconverter will be brought into step after an interruption of power. Theresulting connections are now illustrated in Fig. 3 from which it willbe seen that single phase power is supplied to onewinding 21' of thephase converter, thereby causing this machine to run as a single phaseinduction motor, driving the machine 30 as an exciter.

It should be noted that the excrter is not the frequency of slip, willassist in building.

up the field. After. the exciter field has been thus built up, it willfurnish sufiicient current as a generator to the winding 25 of theconverter to draw the same into synchronous speed, which latter will bemaintained as long as the machines so run.

Although I have herein described whatI now consider to be the preferredform of my invention, I do not wish to be limited to the exactarrangement shown and the method described, but seek to cover in theappended claims all those modifications Which come within the true scopeand spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. The combination with a dynamo-electric machine adapted to operate,either as a motor or as a generator and comprising an armature and aplurality of field windings, of means for connecting said armature inseries with one of said field windings "during the motor operation andfor connecting said armature in series with another of said fieldwindings and for short circuiting the first *mentioned field windingduring the generator operation.

2. In combination, a source of alternating current, a dynamo-electricmachine provided with an exciting winding and adapted to be operatedfrom said source, means for starting said machine and thereafterfurnishing exciting current thereto, comprising a second dynamo-electricmachine mechanically connected to the first machine and provided withtwo field windings wound in opposition and each adapted to be connectedin series with its armature, means for connecting the saidsecond machineto said source of alternating current to drive the same as a motor withone of said field windings in series with the armature, and means forconnecting the second machine to the exciting winding of the firstmachine with the other of said field windings in series with thearmature and for short-circuiting said motor field winding.

In witness whereof, I have hereunto set my hand this 5th day of August,1916.

\ ERNST F. W. ALEXANDERSON.

